1. Field of the Invention
This disclosure relates to a roller member used for an image forming apparatus, a roller supporting mechanism provided with the roller member, and the image forming apparatus.
An image forming apparatus is an apparatus that forms images on recording media. Examples of an electrophotographic image forming apparatus include, for example, electrophotographic copying machines, electrophotographic printers (LED printers, laser beam printers), facsimile apparatuses, and word processors.
2. Description of the Related Art
In the related art, an electrophotographic image forming apparatus (hereinafter, referred to as an image forming apparatus) is provided with a process device having a photosensitive drum (electrophotographic photosensitive drum), which is an image bearing member and configured to act on the photosensitive drum. Examples of the process device include a voltage application apparatus configured to apply electric charge on the photosensitive drum, a developing device configured to supply developer (hereinafter, referred to as “toner”) to the photosensitive drum, and a cleaning device configured to clean toner failed to be transferred and remaining on a surface of the photosensitive drum.
Examples of a charging device in the voltage application apparatus include a roller charging system using a conductive roller. In the roller charging system, charging of the surface of the photosensitive drum is achieved by bringing a charging roller, which is a conductive resilient roller, into bias abutment with the photosensitive drum and applying a voltage thereto. The charging roller generally has a form having a resilient layer covering a metallic shaft over the entire area in a longitudinal direction other than both ends (Japanese Patent Laid-Open No. 2013-109209). Examples of the metallic shaft of the charging roller include a form using a cylindrical-shaped metallic shaft (Japanese Patent Laid-Open No. 2010-230748).
In the case of manufacturing the cylindrical-shaped metallic shaft by pressing a metallic plate, a mating portion (an opposing area where one end portion and the other end portion of the metallic plate oppose each other) extending in an axial direction is present on the metallic shaft. Here, in this configuration, in order to increase the strength of the metallic shaft, a configuration in which projections and depressions are provided alternately on the mating portion and one end portion and the other end portion of the metallic plate are engaged by the depressions and the projections is conceivable.
In this case, by providing the projections and the depressions on the mating portion (opposing area), dimensional accuracy in a radial and the longitudinal direction (axial direction) of the metallic shaft may be lowered at the time of manufacture of the metallic shaft.
Therefore, in the metallic shaft provided with the depressions and the projections in the opposing area of the metallic plate where the one end portion and the other end portion oppose each other, restraint of lowering of the dimensional accuracy of the metallic shaft is required.